1. Field of the Invention
This invention relates to the purification and separations of liquids and solids and more particularly, it relates to apparatus and process for the treatment of oil wet solids to produce oil-free solids and a recovered liquid having oil values.
2. Description of the Prior Art
The drilling of wells into subterranean formations for the recovery of valuable materials such as petroleum is relatively expensive, both as to the equipment employed in the drilling procedures and in the corollary activities to insure that the environment of the area surrounding the well is not injured. In the drilling of wells for the production of petroleum, large amounts of drill cuttings are produced and carried by the circulating mud that passes through the drilling equipment and then is returned to the earth's surface. At the earth's surface, the drill cuttings are separated from the drilling mud through the use of various mechanical solids control equipment such as, screens, shakers, solid-separators, desanders, mud cleaners, desilters and the like. The drill cuttings from a petroleum formation will contain petroleum or oil, both in suspension and also adhering to the solids separated from the drilling mud. In addition, it is common practice to employ an oil based drilling fluid. The drill cuttings produced by an oil based drilling fluid are rather heavily contaminated by the oil base which is used for preparing the drilling fluid. For example, the drill cuttings separated from the returning drilling mud from such a well drilling operation, may contain 40% by volume of oil carried by the drill cuttings.
The oily drill cuttings can not be discharged directly into a disposal site at the well not only because of their adverse effect upon the environment, but additionally, because the great value of the oil contained in them. It has been a common practice to treat the oil drill cuttings in order to produce a solid material that can be disposed into the environment surrounding the well site without injury to it. One method of treating these oily drill cuttings has been through the use of a chemical washing system. In this system, the oily drill cuttings are treated with various chemicals including detergents with relatively intense mixing. Then, this mixture is resolved into relatively oil-free solids (i.e., the drill cuttings) and a recovered liquid phase which is a mixture of water, oil and the detergents which were employed in the chemical wash system. The solids could be disposed by burial or other means. However, these solids may contain sufficient oil that upon contact with bodies of water, such as surface waters, lakes or the ocean, there will be produced a rainbow effect which is unacceptable relative to preserving the environment in the best possible form. In addition, the liquid phase must be treated to separate the oil from the bulk water phase so that the water portion can be discharged or otherwise disposed without pollution problems. The separated oil can be utilized for various uses such as fuel or be returned into the blending of additional oil based drilling muds and the like.
One objection to the chemical wash system, is its relatively high cost in the amount of above several hundred dollars a day, merely from the chemical requirements.
The chemical wash system is described in U.S. Pat. Nos. 2,266,586, 3,860,019, and 3,766,997. Other methods have been proposed to purify the oily drill cuttings into a solid material that can be disposed of without injury to the environment. For example, various thermal systems for driving the oily phase from the solids of the drill cuttings through the use of thermal energy has been proposed. For example, a type of incineration process can be employed such as described in U.S. Pat. Nos. 3,693,951, 2,266,586 and 4,139,462. In the later patent, the oily drill cuttings are passed through a chamber which is continuously flooded with an inert fluid such as nitrogen gas. The cuttings are heated to elevated temperatures above 500.degree. F. for extended periods of time. Then, these heated cuttings are moved through the chamber until all the volatile materials are vaporized to leave an oil-free solids residue which could be disposed safely in the environment. This thermal procedure is relatively expensive, in that it requires large amounts of an inert gas to prevent internal explosions by the contact with air of the heated solids at excessive temperatures. The relatively large amounts of the inert gas complicate the recovery of liquid materials from the chamber because of the undesired high levels of gas flow into condensers and the like.
The greatest disadvantage in this particular procedure for treating oily drill cuttings, is the danger of explosions in the system should air or other oxidizing gas enter into contact with the heated oil vapors produced by the excessive heating of the oily drill cuttings. Should the flow of inert gas be terminated through accident or inadvertence, air entering in contact with these oily vapors could produce a very serious explosion and fire. Such an arrangement, is not acceptable in the area surrounding an oil well, especially while it is being drilled.
The above described prior procedures for treating oily drill cuttings have other serious disadvantages, especially when they are to be employed on offshore drilling platforms. For example, large amounts of chemicals must be transported at great expense to offshore facilities. In addition, these offshore platforms do not have any surplus of steam, gas, electrical or other energy sources. Thus, a procedure for treating the oily drill cuttings must be self-sufficient relative to the operations on the offshore platforms. Stated in a different manner, the treatment procedure for oily drill cuttings must not place any burden upon the facilities of the offshore platform. In addition, the treatment procedure for the oily drill cuttings must be safe in operation, not require excessive operator time, operate without interference or hindrance to the drilling operations conducted on the offshore platform while yet producing an oil-free solids from the drill cuttings which can be disposed of safely and without any injury to the environment at the drilling site. In addition, the system for the treatment of oily drill cuttings at the drilling site, and especially on an offshore platform, must not require a constant supply requirement of chemicals, fuel, nitrogen or other materials for its operation.
The present dryer system is arranged to satisfy all of the requirements for use in connection with the drilling of an oil well, and especially in connection with its placement upon an offshore platform, without the disadvantages of the prior art and in addition, providing for self-sufficient operation with minimum operator attention, and absolute fail-safe operation.